During the last decades, a charging system well known by the name “bell-less top” (BLT) has found widespread use throughout the world for charging blast furnaces. This system includes a charging device with a distribution chute that is mounted rotatable about the vertical furnace axis and pivotable about a horizontal axis for distributing bulk material on the stockline. The charging device is further provided with a gear mechanism cooperating with respective drives for rotating and pivoting the distribution chute according to the desired charging profile. By rotating the chute about the vertical furnace axis and by varying the inclination of the chute, it is possible to direct bulk material (burden) to virtually any point of the charging surface. Accordingly, besides many other advantages, the BLT system enables a wide variety of charging profiles due to its versatility in distributing the burden on the charging surface.
An example of the above type of charging device is disclosed in U.S. Pat. No. 3,880,302. With respect to FIG. 2, this patent discloses a charging device for distributing bulk material in a shaft furnace. This device comprises a stationary housing 204 supporting a rotatable structure 228, 234, 236 that carries adjustable distribution means in the form of a pivotally adjustable distribution chute 208. Rotation of the rotatable structure 228, 234, 236 allows circumferential distribution of bulk material whereas pivotally adjusting the distribution chute 208 allows radial distribution of bulk material. In this device, a first rolling bearing comprises a first stationary race 214 bearing, by groups of rollers 216, 218, 220, a first rotary race that is coupled to a first gear ring 212. The gear ring 212 cooperates with a first drive 1 for rotating the rotatable structure 228, 234, 236. A second rolling bearing comprises a second stationary race 254 bears, by groups of rollers 256, 258, 260, a second rotary race coupled to a second gear ring 242. The second gear ring 242 cooperates with a second drive 25 for adjusting the pitch angle of the distribution chute 208. Charging devices based on the design disclosed in U.S. Pat. No. 3,880,302 have proven very successful and consequently found widespread use in industry over the last decades. Nevertheless, their design leaves room for further improvement, e.g. as regards overall construction height of the charging device. In fact, as seen in FIG. 2 of this patent, a certain minimum height is necessarily taken up by the charging device due to space required for the disposition of its numerous components, e.g. gear rings 212, 242, bearings 216, 218, 220; 256, 258, 260 and gear boxes 270, 272 for rotating and pivoting the chute 208. Chinese utility model no CN 2595815 Y proposes a charging device with a housing supporting a rotatable structure that carries a distribution chute in pivotally adjustable manner. In this design, a first gear ring for rotating the structure has a diameter considerably smaller than an inwardly facing second gear ring for pivoting the chute. Thereby, a certain reduction in height could be achieved since the first gear ring and the second gear ring can be arranged in vertically overlapping manner, i.e. at substantially identical axial locations. With the known prior art devices, assembly and disassembly of the charging device, especially for initial on-site installation but also for maintenance, is however relatively complicated and time-consuming among others due to the arrangement of rolling bearings and gear rings.